Although insulin has profound effects on the metabolism of many tissues, the mechanism(s) through which insulin regulates intracellular processes, such as RNA and DNA synthesis in the nucleus, is not understood. At present, insulin is known to act at the plasma membrane of cells, but whether insulin also acts in the interior of the cells is not known. The Principal Investigator has performed preliminary experiments which have demonstrated that insulin binding sites are present on nuclei prepared from rat liver. This finding suggests that, in addition to the plasma membrane, the nucleus may also be a site of action for insulin. The proposed research will attempt to characterize the physical-chemical nature of this binding reaction and also compare binding of insulin to the nucleus with binding at the plasma membrane. Normal and insulin-resistant animals will be employed. In addition, studies will be undertaken to determine the subnuclear localization of the insulin binding site. Nuclear membranes, chromatin, DNA, RNA, histone, and proteins extracted from nuclei with 0.4 M KCl will be investigated. Other studies will determine whether nuclei from other mammalian tissues, such as brain and lymphocytes, and nonmammalian tissues, such as cells of Drosophila, have binding sites for insulin. Finally, studies with intact cells will attempt to determine the mechanism by which insulin enters the cell and binds to nuclei.